8-1 neighbor ip-address peer-group-name advertise-map route-map-name1 non-exist-map route-map-name2

8-1 neighbor { ip-address peer- group - name } advertise-map route-map-name1 non-exist-map route-map-name2

Syntax Description:

• ip-address Neighbor's IP address.

• peer-group-name Name of the peer group. See section 8-19.

• route-map-name1 Route map that identifies the secondary prefix to advertise only if the primary prefix referenced by route-map-name2 disappears.

• route-map-name2 Route map that identifies the primary prefix to advertise. If this route disappears, the secondary prefix referenced by route-map-name1 is advertised.

Purpose: The primary prefix referenced by route-map-name2 is advertised to BGP peers if the prefix is in the BGP table. If the network is directly connected, the network or redistribute connected command can be used to place the primary network in the BGP table. If the primary prefix is learned via an IGP, the redistribute IGP command installs the prefix in the BGP table. The prefix may be learned from a BGP peer and is automatically placed in the BGP table. The primary prefix is advertised until it disappears from the BGP table. This can happen if the network goes down or if the advertisement for this network is no longer being received. When the route disappears, the prefix referenced by route-map-name1 is advertised. If the primary network reappears in the BGP table, it is again advertised, and the secondary prefix is suppressed.

Cisco IOS Software Release: 12.0

Configuration Example: Advertise the Primary Route While Suppressing the Secondary Route

The goal of this example is to illustrate the mechanics of the neighbor advertise-map command. In Figure 8-1, Router A advertises network 156.26.32.0/24 if the route is up. If network 156.26.32.0/24 goes down, network 144.223.8.0/24 is advertised.

Figure 8-1. Illustration of the neighbor advertise-map Command

 Router A  interface loopback 0   description primary prefix   ip address 156.26.32.1 255.255.255.0   !   interface loopback 1   description secondary prefix   ip address 144.223.8.1 255.255.255.0   !   router bgp 1   network 156.26.32.0 mask 255.255.255.0   network 144.223.8.0 mask 255.255.255.0   neighbor 10.1.1.2 remote-as 1   neighbor 10.1.1.2 advertise-map secondary non-exist-map primary   !   access-list 1 permit 156.26.1.0 0.0.0.255   access-list 2 permit 144.223.8.0 0.0.0.255   !   route-map primary permit 10   match ip address 1   !   route-map secondary permit 10   match ip address 2   ___________________________________________________________________________  Router B  router bgp 1   neighbor 10.1.1.1 remote-as 1   !  

Two loopbacks have been created on Router A to simulate the primary and secondary prefixes. Both prefixes must be in the BGP table. The two network commands on Router A install the prefixes in the BGP table. If both of the loopback interfaces are up, the primary and secondary prefixes are in the BGP table on Router A. The advertise-map command prevents the secondary prefix from being advertised to BGP peers as long as the primary prefix is in the BGP table. If the primary prefix disappears from the BGP table, the secondary prefix is advertised.

Verification

Verify that the primary and secondary prefixes are in the BGP table on Router A:

 rtrA#  show ip bgp  BGP table version is 15, local router ID is 156.26.32.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric LocPrf Weight Path *> 144.223.8.0/24   0.0.0.0                  0         32768 i *> 156.26.32.0/24   0.0.0.0                  0         32768 i 

Verify that only the primary prefix is being advertised to Router B:

 rtrB#  show ip bgp  BGP table version is 23, local router ID is 10.1.1.2 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric LocPrf Weight Path * i156.26.32.0/24   10.1.1.1             0    100      0 i 

You can also view the effect of advertise-map by examining specific entries in the BGP table.

 rtrA#  show ip bgp 144.223.8.0   BGP routing table entry for 144.223.8.0/24, version 29   Paths: (1 available, best #1)   Not advertised to any peer  Local     0.0.0.0 from 0.0.0.0 (156.26.32.1)       Origin IGP, metric 0, localpref 100, weight 32768, valid, sourced, local,2 rtrA#  show ip bgp 156.26.32.0   BGP routing table entry for 156.26.32.0/24, version 28   Paths: (1 available, best #1)   Advertised to non peer-group peers:   10.1.1.2  Local     0.0.0.0 from 0.0.0.0 (156.26.32.1)       Origin IGP, metric 0, localpref 100, weight 32768, valid, sourced, local,2 

To demonstrate the operation of the advertise-map command, we need to make the primary prefix disappear from the BGP table on Router A by shutting down loopback interface 0 on Router A:

  int loopback 0   ip address 156.26.32.1 255.255.255.0   shutdown  

The primary route should disappear from the BGP table on Router A:

 rtrA#  show ip bgp  BGP table version is 16, local router ID is 156.26.32.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric LocPrf Weight Path *> 144.223.8.0/24   0.0.0.0                  0         32768 i 

With the primary route gone, the secondary route should be advertised to Router B:

 rtrB#  show ip bgp  BGP table version is 23, local router ID is 10.1.1.2 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric LocPrf Weight Path * i144.223.8.0/24   10.1.1.1             0    100      0 i 

The specific entries for the primary and secondary prefixes show the effect of non-exist-map:

 rtrA#  show ip bgp 144.223.8.0   BGP routing table entry for 144.223.8.0/24, version 31   Paths: (1 available, best #1)   Advertised to non peer-group peers:   10.1.1.2  Local     0.0.0.0 from 0.0.0.0 (156.26.32.1)       Origin IGP, metric 0, localpref 100, weight 32768, valid, sourced, local,2 rtrA#  show ip bgp 156.26.32.0  % Network not in table 

Troubleshooting

1. Verify that the BGP neighbors are in the Established state using the show ip bgp neighbors command.

   If the neighbor relationship is not in the Established state, see section 8-23.

2. Ensure that the primary and secondary prefixes are in the BGP table using the show ip bgp command.

3. If the primary and secondary routes are in the BGP table, go to Step 5.

4. If the primary and secondary routes are not in the BGP table, do the following:

   1. If the primary and secondary routes are directly connected, static, or redistributed from another protocol, check either the network commands or redistribute commands under router BGP. If you are using the network command, there must be an exact match between the network command (prefix/mask) and the IP routing table entry (prefix/mask). Go to Step 2.

   2. If the primary and secondary routes are learned from a BGP neighbor, check to see if the routes are in the neighbor's BGP table. If the routes are in the neighbor's BGP table and the BGP neighbors are in the Established state, check for any filters that might be blocking the routes. Go to Step 2.

5. Verify that route-map-name1 is associated with the secondary route and that route-map-name2 is associated with the primary route.

6. Verify that the route maps exist and are using the proper syntax.

7. Verify that the access lists referenced by the route maps exist and are using the proper syntax.

8. Check for any filters that might be blocking the advertisement of the primary route or secondary route if the primary is down.

9. Debug the BGP updates between the neighbors.

   1. Use the debug ip bgp updates command to verify that the primary is up and is being advertised.

       rtrA#  1w6d: BGP: route up 156.26.32.0/24   1w6d: BGP: nettable_walker 156.26.32.0/24 route sourced locally  1w6d: BGP: 10.1.1.2 computing updates, neighbor version 27, table version 28, starting at 0.0.0.0  1w6d: BGP: 10.1.1.2 send UPDATE 156.26.32.0/24, next 10.1.1.1, metric 0, path  1w6d: BGP: 10.1.1.2 1 updates enqueued (average=55, maximum=55) 1w6d: BGP: 10.1.1.2 update run completed, ran for 8ms, neighbor version 27, start version 28, throttled to 28, check point net 1w6d: BGP: scanning routing tables 1w6d: BGP: Condition primary changes to Withdraw  1w6d: BGP: net 144.223.8.0 255.255.255.0 matches ADV MAP secondary: bump version to   29   1w6d: BGP: nettable_walker 144.223.8.0/24 route sourced locally  1w6d: BGP: 10.1.1.2 computing updates, neighbor version 28, table version 29, starting at 0.0.0.0  1w6d: BGP: 144.223.8.0 255.255.255.0 matches advertise map secondary, state:   Withdraw   1w6d: BGP: 10.1.1.2 send UPDATE 144.223.8.0/24 - unreachable  

   2. Use the debug ip bgp updates command to verify that the primary is down.

        1w6d: BGP: route down 156.26.32.0/24   1w6d: BGP: no valid path for 156.26.32.0/24   1w6d: BGP: nettable_walker 156.26.32.0/24 no best path  1w6d: BGP: 10.1.1.2 computing updates, neighbor version 25, table version 26, starting at 0.0.0.0  1w6d: BGP: 10.1.1.2 send UPDATE 156.26.32.0/24 -- unreachable  1w6d: BGP: 10.1.1.2 1 updates enqueued (average=27, maximum=27) 1w6d: BGP: 10.1.1.2 update run completed, ran for 8ms, neighbor version 25, start version 26, throttled to 26, check point net  1w6d: BGP: scanning routing tables   1w6d: BGP: Condition secondary changes to Advertise   1w6d: BGP: net 144.223.8.0 255.255.255.0 matches ADV MAP secondary: bump version to   27   1w6d: BGP: nettable_walker 144.223.8.0/24 route sourced locally  1w6d: BGP: 10.1.1.2 computing updates, neighbor version 26, table version 27, starting at 0.0.0.0  1w6d: BGP: 144.223.8.0 255.255.255.0 matches advertise map secondary, state:   Advertise   1w6d: BGP: 10.1.1.2 send UPDATE 144.223.8.0/24, next 10.1.1.1, metric 0, path